5. Do pull-request from own repo: feature/something to upstream: master.

At this moment, only 1 commit.

6. Get the review from upstream people.

7. Push modification after the review to own repository: feature/something

At this moment For example 3 commits.

we should do "rebase" & squash after every modification, and unify 1 commit from these commits.

That means

$ git rebase -i commit_hash_before_your_modification

pick
s
s
...

$ git push origin feature/somthing -f

origin is own repository.
And upstream's pull-request page is no problem after above command.
The previous modification's comment and file & lines are saved on the page.
And total commit & file difference info was updated.

So, again.
We should do "rebase" & squash after every modification, and unify 1 commit from these commits, for pull-request.